Safety device for motor driven tools



J. M. HADFIELD 1,910,217

SAFETY DEVICE FOR MOTOR DRIVEN TOOLS Filed Oct. 10, 1931 mil 11 "J Z2 M g [I M};

Patented May 23, 1933 SAFETY DEVICE FOR MOTOR DRIVEN 'I JOSEPH M. HADFIELD, OF CHICAGO, ILLINOIS OOLS Application filed October 10, 1931. Serial No. 568,196.

- The present invention relates to safety devices for motor driven tools and is particularly concerned with the provision of devices for preventing the usersof motor driven tools from leaving the usual metal pin which is used for holding the drive shaft while cutters are adjusted, in the shaft when the motor is started.

The present invention is applicable to motor driven tools of various kinds, and therefore the tool is merely illustrated diagrammatically. It is customary in the adjustment of the cutters on many motor driven tools to insert a metal pin in a hole in the drive shaft or in some part of the mechanism for positively preventing rotation of the shaft while the cutters are being adjusted. This permits the more convenient adjustment of the cutters, since the shaft is held in fixed position, and it also prevents any possibility of the shaft rotating the cutters and possibly injuring the operator.

Such metal pins are frequently drive shaft when the operator has adjusted the cutters, and when the motor circuit is closed the motor is burned out due to the fact that its armature cannot rotate and there is no counter-electromotive force to limit or regulate the current in the motor. hen this happens, a great deal of expense is involved because the motor must be practically replaced with a new motor and one of the objects of the invention 'is the provision o a safety system adapted to positively prevent the mistake of leaving the metal pin in the shaft when the motor circuit is closed.

Another object of the invention is the provision of an improved switching device which is adapted to be placed in the circuits of any electric motor for the purpose of controlling the motor circuit by means of the usual metal pin which is employed for holding the shaft in fixed position when the, cutters are adjusted.

Another object of the invention is the provision of an improved switching device of the class described which will prevent the operator of a motor driven tool from leaving the metal pin in the drive shaft.

Another object of the invention is the proleft in the vision of an improve the class described w constructed out of ordi such as a conduit outlet box and nary stock the accessories for installing conduits.

Another ob ect of the invention is the provision of an improved swit the class described which is sturdy, ical and capable of being manu of performing its cheaply and capable tions for a long period cessity for repair.

d switching device of hich is adapted to be materials usual ching device of economfactured funcof time without ne- Other objects and advantages of the int from the following venti'on will be apparen description and from drawing, in wh1ch similar character erence indicate similar views.

the accompanying s of refparts of the several Referring to the single sheet of drawing,

Fig. 1 is a diagrammatic view of the safety system with the motor tion;

circuit in open posi- Fig. 2- is a transverse sectional view taken through the switch casing,

showing the switching device in partial section with the switch in closed pos1t1on.

l' f tl 1L 1g. is a airin ia i am 0 ano iei iiication.

mod-

Fig. l is a vertical sectional view taken on the plane of the line i-* the arrangement venting rotation of the shaft.

Referring to Fig. 1,

erably includes an el reduction, speed increasing gearing 12, some form of cutter 1 device indicated in its e The mechanis form of speed mer al 14:.

driven tool may be p ture 15 in the drive sl ister with an aperture 16 in th 11, so that the metal through the apertures 1 drive shaft 12 in the safety sys ectric motor 10, any

speed chan 11, a drive 4: of Fig. 1, showing 30 of the metal pin for pretem prefge or shaft 3, and a switching ntirety by the num of the motor rovided with an aperiaft 12 adapted to rege gear casing 11 17 may be inserted ably include the conductors 18 and 19 conductors 21 and 22 h 20. om the motor 1 5 and 16 to hold the fixed position.

The control circuits for the motor preferleadsupply and The 0 lead 62 is provided with a spring for normally urging it to open position, and it will be noted that when the push button 62 is actuated, a circuit may be traced from the second phase to the third phase, through the magnet 50. The magnet then draws up its armature 51 and closes the starter switch contacts in all three phases, as well as contacts 55, 59.

The other end of the magnet coil 50 is connected by connector 66 to one of the contacts 67 of the push button 63. The other fixed contact 58 of push button 63 is connected by conductor 69 in series with the safety switch 14:. A conductor 70 leads from the safety switch 14 to the third phase of the three phase line.

Push button 63 is normally urged to closed position by a spring, and it will be observed that the closing of contacts 55, 59 short-circuits the push button 62. l/Vhen push button 62 is released, therefore, the magnet 50 remains energized until push button 63 is pushed, breaking the magnet circuit and deenergizing the magnet, which results in the release of armature 51 and the opening of the three phase contacts.

It will thus be observed that the present device may also be used with a motor starter in a three phase circuit, or it may be used with motor starters for single phase circuits. Since the safety switch is in series with the main circuit of the magnet coil 50, it is impossible to energize the magnet 50 without placing the pin 17 back in the safety switch box.

It might be thought that the operator could quickly see that the machinery was not moving when he closes the switch 20, thereby reminding him that he has not removed the pin 17, but in many cases the mechanism moves so fast that it is difficult to distinguish whether it is moving or standing still, and the failure to remove the said pin 17 in the devices of the prior art almost inevitably results in the burning out of the motor.

lVhen the present device is used, the operator is reminded that the pin 17 must be placed in the switching device 1d, and furthermore, a definite place is provided for keeping the pin 17 so that it is not lost.

The present device positively precludes operators from burning out the motor by means of the pin 17 and the manufacturer is thus assured that there Wlll be no necessity for replacement or repair of motors on this account and no delay caused by the burning out of motors in this manner. It will be evident that the saving of a single motor is suflicient to pay for agreat many safety devices of the class described and that the present safety system is therefore highly advantageous in any factory where such metal pins are employed in holding a drive shaft.

While I have illustrated a preferred embodiment of my invention, many modifications may be made without departing from the spirit of the invention, and I do not wish to be limited to the precise details of constrnction set forth, but desire to avail myself of all changes within the scope of the appended claims.

Having thus described my invention, 1 claim new and desire to secure by ters Patent of the United States, is:

what Let- In a safety system, the combination of an el ctric motor driven machine having a driven shaft with a supporting framework, said h ft having an aperture and said framework aving a registering aperture, a metal memer adapted to be received in said apertures or r Xedly securing said driven shaft against n, supply circuits for energizing said and a normally open electric switch for controlling said supply circuits said switch being adapted to be closed by the placing of said metal member in predetermined position with respect to said switch whereby the motor cannot be started until said metal member is removed from said apertures and placed in said switch.

2. In a safety system, the combination of an electric motor driven machine having a driven shaft with a supporting framework, said shaft having an aperture and said framework having a registering aperture, a metal member adapted to be received in said apertures for fixedly securing said driven shaft against rotation, supply circuits for energizing said motor, and normally open electric switch for controlling said supply circuits, said switch being adapted to be closed by the placing of said metal member in predetermined position with respcct to said switch whereby the motor cannot be started until said metal member is removed from said apertures and placed in said switch, and means for controlling said motor comprising an electromagnetic switch located in the supply circuit of said motor. a push button switch for closing the circuit through the electromagnet of said switch, an auxiliary contact carried by said electromagnetic switch for shunting said push button switch, and an auxiliary push button for opening the circuit through said electromagnet to effect an opening of said electromagnetic switch.

3. .ln a safety system, the combination of an electric motor driven machine having a driven shaft with. a supporting framework, said shaft having an aperture and said framework having a registering aperture, a metal member adapted o be received in said apertures for fixedly securing said driven shaft against rotation, supply circuits for energizing said motor, a normally open electric switch for controlling said supply circuits, said switch being adapted to be closed by the placing of said metal member in predetermined position with respect to said switch whereby the motor cannot be started until said'metalimemberis removed from saidaperitures andr placed in 1 said: s

witch, said switch beingenclbsedin a casing having a socket for receiving saidmetal member topreventr actuationbf saidswitch except by said metal member.

I11 witness whereof, I hereunto subscribe myname, this 12th-day of JOSEPH MI September, 1931.

HADFIELD. 

